COS 54-2
Structure and function of insect-flower interaction networks in relation to loss of floral diversity and surrounding landscape context
Studies have demonstrated positive relationships between floral and pollinator diversity in a range of habitat types. The effects of loss of pollinator diversity for plant pollination may be buffered by functional redundancy, whereby remaining species fill the ecological roles of the missing species. However, if entire functional groups are lost, this can result in loss of pollination service and knock-on impacts for the plant community, and further reductions in pollinator diversity. There has been little work on the effects of diversity loss on interactions between plants and their pollinators and pollination function (pollen deposition on the stigma). By sampling insect-flower interactions in 20 low intensity grassland sites in Ireland, we quantified interaction network parameters and related them to pollen deposition (as a proxy for pollination service) and the surrounding landscape composition and configuration.
Specifically, we tested the hypotheses that 1. An increase in grazing intensity and associated reductions in plant diversity result in: a) Reduced pollinator diversity and changes to pollinator community composition; b)Reduced insect-flower interactions and changes to interaction network structure; c) Reduced pollination function; and 2. Pollinator diversity and pollination service varied according to the composition and configuration of surrounding landuse.
Results/Conclusions
Positive relationships between plant and pollinator diversity were confirmed over two sampling seasons. In addition to species diversity, pollinator functional type diversity was also related to plant diversity, with fewer functional pollinator types in sites with low floral diversity. Interaction networks were small, with 6-25 pollinator species and 6-17 plant species per site. Networks displayed low connectance and a relatively high degree of nestedness. Negative relationships between grazing intensity and floral and pollinator diversity were found, and between grazing intensity and pollen deposition in Trifolium repens (white clover): with more grazers, there were fewer pollinator species in a site and reduced pollination service. A negative relationship between connectance and pollen deposition was found; and as networks became more nested, pollen deposition increased. Linkage density was negatively related to grazing intensity and positively with pollen deposition. Each pollinator group responded in a different way to the landscape structure up to 1km from sampling sites with knock-on effects on interaction network structure and pollination service delivery. Understanding relationships between diversity and function at a landscape scale is crucial for a better conservation management decisions; ensuring essential levels of pollination services to both crops and wild plants are maintained.